1. Field of the Invention
The present embodiments relate to an organic thin film transistor, and more particularly, to a method of patterning an organic thin film which prevents the surface of an organic semiconductor layer from being damaged. The present embodiments also provide an organic thin film transistor and an organic electroluminescence display device having an organic thin film transistor that can prevent surface damage and can reduce an off-current of an organic semiconductor layer and a method of manufacturing the organic thin film transistor.
2. Description of the Related Art
Studies on organic thin film transistors (OTFTs) for use in next generation display devices have been actively performed. OTFTs use an organic film instead of a silicon film as a semiconductor layer, and are classified into low molecule organic thin film transistors using oligothiophene and pentacene, and polymer organic thin film transistors using polythiophene, according to the material for forming the organic film.
An organic electroluminescence display device that uses an organic thin film transistor as a switching device includes at least two organic thin film transistors, for example, one switching organic thin film transistor and one driving organic thin film transistor, one capacitor, and an organic light emitting diode having an organic film layer interposed between upper and lower electrodes.
Typically, a flexible organic electroluminescence display device uses a flexible substrate that includes a plastic substrate. The organic electroluminescence display device that uses the plastic substrate has to be manufactured in a low temperature process since the plastic substrate has very low thermal stability.
Accordingly, an organic thin film transistor that uses an organic film as a semiconductor layer has been largely considered as an alternative for the switching device of the flexible organic electroluminescence display device since the organic thin film transistor can be manufactured in a low temperature process.
A pentacene thin film transistor that can reduce the thin film deposition time and improve the hole mobility has been disclosed in Korea Patent Laid-Open No. 2004-0028010. A device structure of an organic thin film transistor and a method of manufacturing the organic thin film transistor that can improve the electrical performance of the transistor have been disclosed in Korea Patent Publication No. 2004-0084427. Also, a thin film transistor that can improve carrier mobility and on/off current ratio by forming a channel region into an organic compound having a radical has been disclosed in Japanese Laid-Open Patent No. 2003-92410.
FIG. 1 is a cross-sectional view of a conventional organic thin film transistor having a top gate structure.
Referring to FIG. 1, a conventional organic thin film transistor 10 includes a gate electrode 12 formed on a substrate 11, a gate insulating film 13 formed on the substrate 11 including the gate electrode 12, source and drain electrodes 14 and 15 formed on the gate insulating film 13, and a semiconductor layer 16 formed on the source and drain electrodes 14 and 15 and the gate insulating film 13.
In the conventional organic thin film transistor 10 having the above structure, the semiconductor layer 16 includes an organic semiconductor layer, and the unpatterned semiconductor layer 16 is formed on the entire surface of the substrate 11. Therefore, there is a problem of a leakage current due to the accumulation of carriers, for example, holes, between the semiconductor layer 16 and the gate insulating film 13.
To solve the above problem, when the organic semiconductor layer is pattern using an ablation method, as depicted in FIG. 2, thermal denaturation or recasting by a laser can occur at edge portions of the patterned semiconductor layer.